from machine import Pin
from time import sleep

#list
led_pins=[0,1,2,3]

#list comprehension
led=[Pin(pin,Pin.OUT)for pin in led_pins]
while True:
    for i in range(4): #range formula is n-1 where n=4 starting from 0
        led[i].value(1)
        sleep(1)
        led[i].value(0)
        sleep(1)


        

    #another way

    #led.on()
    #sleep(1)
    #led.off()
    #sleep(1)